A conventional collision sensing technique is disclosed in an impulse sensor of U.S. Pat. No. 4,948,929. The impulse sensor includes two contact terminals disposed in a case body filled with magnetic fluid, a conductive body held floating in the magnetic fluid, and two magnetic components disposed on two opposite outer sides of the case body. In a normal situation, the conductive weight is held floating in the magnetic fluid at the center of the case body. When the impulse sensor is subjected to an impact, the conductive weight is forced to move toward the contact terminals due to inertia so as to electrically interconnect the contact terminals, so that an impact signal can be generated. However, the impulse sensor can only detect impact from a single direction. If the impact does not take place at the predetermined direction, the impulse sensor cannot detect the impact.
Referring to FIGS. 1 and 2, another conventional collision sensing technique is disclosed in an eight-directional induction starting device for a collision sensor of Chinese Patent Publication No. CN102074411A. The eight-directional induction starting device includes an inner magnetic ring 11, an outer magnetic ring 12, two bearings 13 respectively disposed above and beneath the inner magnetic ring 11, an insulating housing 14 surrounding the inner and outer magnetic rings 11, 12 and the bearings 13, and two conductive cover plates 15 respectively disposed above and beneath the insulating housing 14.
By electrically connecting the inner and outer magnetic rings 11, 12 to different electric potentials, when the eight-directional induction starting device is subjected to an impact, the inner magnetic ring 11 is forced to move toward the outer magnetic ring 12 so as to contact and electrically connect with the same, so that an impact signal can be generated.
However, the eight-directional induction starting device can only detect whether an impact has occurred, but not the direction of impact. Furthermore, in order to enhance the sensitivity of the device, the bearings 13 are disposed above and beneath the inner magnetic ring 11 to reduce friction during sliding movement of the inner magnetic ring 11, so that the overall structure of the device is complicated. Moreover, in order to maintain the inner magnetic ring 11 in an electrical connection state, the bearings 13 and the cover plates 15 must be made of electrically conductive materials. This enhances the risk of electric shock.
Referring to FIGS. 3 and 4, a conventional tilt sensor, as disclosed in Japanese Patent Publication No. JP2009117137, includes a first housing 16, a movable contact 17, two fixed contacts 18, two fixed contacts 20, and a second housing 19. When tilted, the movable contact 17 moves to contact one of the fixed contacts 18 and a corresponding one of the fixed contacts 20 to electrically interconnect the two and generate a signal. With the fixed contacts 18, 20 being disposed transversely of each other, an inclination state of the tilt sensor and impact from four directions can be detected. However, when the impact only takes place along a horizontal direction but not along a top-bottom direction, the movable contact 17 cannot be moved to contact one of the fixed contacts 18 and a corresponding fixed contact 20, so that the tilt sensor cannot detect the direction of impact.